DESCRIPTION OF THE PRIOR ART
Polyurethane foams produced by the reaction of a polyether polyol with an isocyanate usually in the presence of a catalyst, surfactant and blowing agent are well known and generally referred to as polyether based polyurethane foams. Suitable reactants for producing polyurethane foam are well known and are generally disclosed in a monograph entitled "Polyurethanes, Chemistry and Technology" by J. H. Saunders and K. C. Firsch, 1962 published by Inter Science Publishers. Advances in polyurethane chemistry since the publication of the monograph are well known to those skilled in the art. Methods of producing polyether based polyurethane foam with flexible, semi-rigid or rigid properties are disclosed in U.S. Pat. No. 3,194,773 issued July 13, 1965 to F. Hostettler, entitled "Process of Making Polyurethane Foams." The Hostettler Patent discusses the effect of molecular weight and viscosity of polyether polyols upon the physical properties of the polyurethane foam produced from the polyether polyol.
Other patents that generally teach the characteristics of polyether polyols, isocyanates and other reactants with respect to polyurethane foams are U.S. Pat. No. 3,383,351 issued to P. Stamberger which concerns polymer polyols, and U.S. Pat. No. 3,454,505 issued to James Cross et al. which discuss various polyether polyols suitable for making polyurethanes.
Polyether polyols having a functionality of at least 2.0 are known to be suitable for producing flexible polyurethane foams and accordingly are suitable for practicing the present invention. The term "polyether polyol" is intended to include linear and branched polyethers (having ether linkages), and containing at least two hydroxyl groups. Preferred polyethers are the polyoxyalkylene polyols particularly the linear and branched poly(oxethylene)glycols, poly(oxypropylene)glycols and their co-polymers.
Polyether polyols have at least two active hydrogen atoms, (i.e., hydroxyl groups).
The term polyisocyanate refers to particularly those isocyanates which have previously been suggested for use in the preparation of polyurethane foams and includes di- and polyisocyanates and prepolymers of polyols and polyisocyanates having excess isocyanate groups available to react with additional polyol.
Chemically, the organic polyisocyanates which may be employed include both aromatic and aliphatic isocyanates. As used herein the term aliphatic isocyanate includes both aliphatic and alicyclic compounds as well as the aliphatic-like compounds--i.e., those which although they contain an aromatic ring, react as an aliphatic compound, due primarily to the fact that the isocyanate group is not attached directly to the ring.
The amount of polyisocyanate employed is frequently expressed by the term "Index" which refers to the ratio of the actual amount of isocyanate in the reaction mixture to the theoretical amount of isocyanate required for reaction with all the active hydrogen containing compounds present in the reaction mixture multiplied by 100. For most applications the Index is in the range of from about 70 to about 150, preferably from about 90 to about 130.
Catalysts that may be used to accelerate the polyolpolyisocyanate reaction include, for example, amines and metal salts the latter including both inorganic and organic salts. The catalyst may be either a single compound or a mixture of two or more compounds. It is especially preferred to employ, as the catalyst, an organotin salt or a tertiary amine.
The amount of catalyst employed may be varied over a wide range depending upon the formulation employed and the type of catalyst, all of which is well-known to those skilled in the art. For most applications the catalyst, either as a single compound or as a mixture of compounds, is employed in an amount equal to from about 0.01 to about 5.0 parts by weight per 100 parts by weight of polyol in the foam forming composition.
Polyurethanes are used in both the unfoamed and the so-called "foam" form. In general a foamed polyurethane is produced when low boiling liquids, gaseous blowing agents or inflatants are incorporated into or generated by the polyurethane foaming reactants. Often the heat of reaction causes the low boiling liquid or gaseous blowing agent to volatilize, thus foaming the composition. In some instances a technique generally referred to as frothing is employed in which case the boiling point of the blowing agent is chosen to be below room temperature. In this way the composition can be made to foam even before any substantial reaction between the polyol and the polyisocyanate reactants has occurred or before any heat is evolved.
Blowing agents which may be employed include, for example, water either alone or admixed with other components--e.g., as an aqueous solution of the catalyst. When water is employed it reacts with an excess of the polyisocyanate to generate carbon dioxide thereby resulting in a foam. Carboxyl containing compounds may also be included as a source of carbon dioxide.
Other useful blowing agents include the chlorinated and fluorinated alkanes having from 1 to about 3 carbon atoms such as the chlorofluorothanes; pentane; hexane; methylchloroform; butane; methylene chloride; difluoro-1,2-dichloroethylene and diethyl ether.
The amount of blowing agent employed can be varied over a wide range as is well-known to those skilled in the art depending primarily upon the density desired in the foam product. For most applications the blowing agent is employed in an amount equal to from about 2 to about 15 parts by weight per 100 parts by weight of polyol in the foam forming composition.
When blowing agents are included in or generated by the polyurethane reactants, there is also frequently included in the composition a surfactant type stabilizer the function of which is to control the amount and quality of the foamed polyurethane obtained. Without the stabilizer the foams may either collapse or contain very large uneven cells.
Representative surfactants which may be employed include:
silicone compounds and silicone oil mixtures such as siloxaneoxyalkylene block copolymers; PA1 polyethylene glycol ethers of long chain alcohols; PA1 tertiary amine or alkylolamine salts of long chain alkyl acid sulfate esters, alkyl sulfonic esters and alkyl arylsufonic acids; PA1 compounds prepared by the sequential addition of propylene oxide and ethylene oxide to propylene glycol; PA1 castor oil sulfonate; PA1 ethylene oxide adducts of sorbitol; PA1 mono-esters of long-chain fatty acids; and PA1 ethylene oxide adducts of alkyl phenols.
The amount of surfactant employed can be varied over a wide range depending, for example, on the foam-forming composition employed and the properties desired in the foam product. For most applications, the surfactant is employed in an amount equal to from about 0.1 to about 10 parts by weight per 100 parts by weight of the polyol in the foam-forming composition.